Published in “PLOS ONE,” the research analyzed whether happiness and other emotions are spread from person to person on social networks such as Facebook.

Using data from more than one billion anonymous status updates among more than 100 million Facebook users in the 100 most populous cities in the United States, the study found that positive posts beget positive posts, while negative posts beget negative ones.

According to the research, positive Facebook posts are more influential than negative ones, spreading the positivity among others. Each additional negative post yields 1.29 more negative posts among friends, while each additional positive Facebook post yields an additional 1.75 positive posts among friends, the study deduced.

In order to measure the emotional content of each post, UC San Diego says researchers used an automated text analysis software program called the "Linguistic Inquiry Word Count."

The study also found that rainy weather changes the mood of Facebook posts – and that mood change can be contagious. The research says rainy weather increases the number of negative posts by 1.16 percent and decreases the number of positive posts by 1.19 percent.

Upon analyzing friends living in different cities as those posting about the rain, researchers found that the moods of those being rained on impacted the moods of their dry friends.

“For every one person affected directly, rainfall alters the emotional expression of about one to two other people, suggesting that online social networks may magnify the intensity of global emotional synchrony,” the study cites.

“Our study suggests that people are not just choosing other people like themselves to associate with but actually causing their friends’ emotional expressions to change,” said lead author Fowler. “We have enough power in this data set to show that emotional expressions spread online and also that positive expressions spread more than negative.”

Fowler said that in today’s digitally-connected world, it’s important to learn what can be transmitted through social media – including how much emotion can actually spread through social networks such as Facebook.

“It is possible that emotional contagion online is even stronger than we were able to measure,” he said.

This could have widespread implications, according to the researchers who write:

“[Emotions] might ripple through social networks to generate large-scale synchrony that gives rise to clusters of happy and unhappy individuals.”

Researchers suggest their findings could impact public well-being.

“If an emotional change in one person spreads and causes a change in many, then we may be dramatically underestimating the effectiveness of efforts to improve mental and physical health,” said Fowler. “We should be doing everything we can to measure the effects of social networks and to learn how to magnify them so that we can create an epidemic of well-being.”

Additional co-authors of the Facebook feelings study include UC San Diego political science graduate student Yunkyu Sohn; Adam D. I. Kramer and Cameron Marlow of Facebook; Massimo Franceschetti, also of UC San Diego’s Jacobs School; and Nicholas Christakis of the departments of sociology and medicine at Yale University.